Method of controlling ferric iron



'11 mow.

mount iron in solutio o is important, s may "oo comm-oiled m the, mannerWhen, ilowovor, the ferric iron solvent of, for example, sulfid Zion:

HOP GERS+FQAS04 %C11S() +2FS0 %-s, 5i f co obemono/l quantity-of ironpresent in the L oiafi'y omit 'i'oz'mo QJHiiiifilfifl as also ofImportance. In ovary involw or words, mmchhons and ope muons toloofiro'iysis; magi-1t o 2 o oontroilo l that the amount P iron, or

m1 a; oh, 4 ovosamom o produced during tho olocfiroly to homo-m filosinuous-3 and who economy xpxtooion of copper shall be substan" ofmooessos of the gonm'ol in iicoteo' The question Oi. in opemmons involvmw m J or concentrates mo. a,

equal 'rbo timt'neodod, when. the resid- "T woro oro oppliod to a,subsequent for the reaction with tho roooostitraaoo'io of tho-ores so"created. 0 "n of my present invontion 11 poly cg cliv oconomiool wottreatment of certain ores. J fiiosolved Mann-e met-ho s of copperleaching to which r introduced with invention. mi as, mo applicable tothe King, pro Hod mixed ores of copper, these being g -w, 40.11lemzmlysis, :Zmfl which portof 1'; copper is present. 3 ox o7, o ferrici1 and the 1. components and the remainder may 4 o i:- foiz'io iron beenregarded having a, seriously dotrizmazztoi ofif'oob on cothodlo51ep-oo'inlon efiiciencyu olo is known thaia, in processes in "which kmsolvent action of ferric, iron. on coppoia? topmmdo is not mode w .1susequont isszzhing operations, this ferns ii'on, as; proool outing;oloctz'olysis, 11' comm- .V xfmhloei o. 0

" "ous condition, if; Wbi

its ooh;

, mid-sofiumo or Goofilm oxidized oomponooto The methods hereindescribed .iiooblo to oro or conoontmisos in lo copper occurs: in thesulfi i oowxonienoo, I shafi generally roits? to the mix-zed ores ofcopper, 1.101121% be undo mood that such ores owed to merely by Way ofofia m'p lo.

*trootmooi; of .n'mteriols of the charozwod, 20, the reducing actions of:iitoonoi: thereof upon ferric salts in I n will ho variable. Generallyspeak Ubhi methods. he most important cause of such varioaiho balance;of iron mu W531 be 116 offering relative propoo with r'oopoct to theoopnions, from time to time, of the oxid constitjoor dissoi ocl I o becontrolled only in uomfis to tho sulfic} constituents in the maone o, ee/n b a21- occuomIa-tim: iorio s rowed. x ught slflfid ores there 01"mm; iron; o-no is commonijr cionoloy may 1 a be *orio'tion in theamounts of To discharging a portion of the main solution ,Qooingoopstimemo, for exampio, pyrrhotite. and treating the some, for copperrecovery is obvious thorofm o, ifilafi, 111 @he iiroab by other methodsthan oiectrolj'oisk mom: of 0m ovfo, eye-11ml method mvolvmg on beingsoon oi-s fifuli" dioxio x the-so Emmm 1 from op'olo to In mothocis whom:115 solvent oc'rloo mow producllvio'o of forric iron by elem ferriciron. is purposol mode so as m port-of the prooooo, 'iurtnorcomphoainoosof oy confirm become necessary. in this ooso, 555v;

onci ms roluotior to a, ferrous form ootzoomam ":fihore may rosuitRoofing money of forms "z'osonfi carbonates, silicates, omzids, or

iron, such excess or deficiency becoming marked after a certain numberof cycles unless there shall be adapted, to meet this difficulty, somemethod which will provide a means of meeting not only a constant excessor deficiency but also a variation from day to day; and it is an objectof my invention to provide a new method of obviating the difficultyreferred to.

The solutions which I use for carrying out my present invention may havea consid erable variation of constituents otherthan iron salts. As tothe iron salts, it has been indicated in the equation above that theusual leaching of mixed or sulfid copper ores by means of liquorscontaining ferric sulfate results in the formation of ferrous sulfate,and it is desirable that the amount of iron in the ferrous form shouldbe, during the electrolysis which follows the leaching, suliicient toact as a depolarizing agent at the anode; and such depolarization isimportant in, for example, methods using anodes of either lead orgraphite, or both. It will, moreover, be obvious thatthe amounts offerric iron should in all cases be sufficient to provide a good solventfor use on the copper compounds leached. The fer ric iron in the leachliquor may, for example, be as high as 1%, or even more; and ferrousiron should subsequently be present in the neighborhood of 1 or more,when the solutions are .in use as electrolyte for the deposition ofcopper. It is accordingly an objcct of my invention to provide a processin which approximately the mentioned respective amounts of ferric andferrous iron shall be present as required.

I have found that the case in which there is a net deficiency of ferriciron during the execution of a process of the general character hereindescribed, may be met by making use of the oxidizing action of finelydivided air brought into intimate contact with the solution. Thisoxidizing action of air in known and does not form a part of my pres entinvention; although I may state that I have found the oxidizingefficiency of air, when properly applied, to be much grezrter than isusually supposed.

My present invention is directed to the opposite situation, in which an.excess of fer- -ric iron is produced; andI have discovered that thissituation may be met in either of two ways, in one of which the totalamount of iron is diminished, andin the other of which the total ironremains a constant. Either or both methods may be used; but, generallyspeaking, the first method may be more applicable to those ores whichcarry appreciable amounts of soluble iron components. It is thus oneobject of my present invention to provide controllable methods for theelimination of iron salts when an excess thereof may accumulate in thecyclic operation of processes of the general character above referredto; and a description of the first of these methods, is as follows:

Fz'rst method- U5 is well known that if solutions containing ferric ironare nearly or quite neutralized and then warmed, a part or all of theferric iron precipitates as indefinite, more or less basic, iron salts.The neutralization of commercial leach liquors would, however, beinconvenient and impracticable, because of the time required and thecost of the acid lost thereby; and the open air heating of solutionscarrying the usual amounts of free acid does not result in theseparation'of appreciable amounts of iron. I have, however, discoveredthat ferric iron components can be precipitated even from commercialleach liquors containing considerable amounts of free acid if only theliquors are kept under pressure, in any suitable apparatus, during theheating. The pressure required is only slight, but apparently somepressure is necessary; for the same solutions heated to the sametemperature without pressure do not yield a preci itate. To meet theconditions of the pro lem, the precipitation of iron obviously should besubject to control, since theamount of the excess will be variable; andthe amount separated by the method re ferred to may be varied bysuitable changes in the conditions. I have found, for example, that theamount of iron which separates is more or less inversely proportional tothe percentage of free acid present; and that it is approximatelydirectly proportional to the temperature and the pressure. Under properconditions, after washing, the precipitate is a relatively insolubleproduct consisting mainly of a basic sulfate or sulfates of iron, inwhich impurities, such as lime, may, in some cases, be present. Ifproperly washed and if precipitated in the presence of sufiicient freeacid, the precipitate will carry no appreciable quantity of copper.

It is one of the objects of my invention to obviate the discarding ofliquors which contain values; but obviously the foregoing method ofcontrolling an excess -of ferric iron will be of particular advantagewhere the ores being treated carry considerable amounts of acid-solubleiron. In the case of such ores, by my method involving the use ofpressure, the amount of solution necessary to be discardedincidentallv'i to; the. leaching of such ores may be con deathlyreduced, or such discarding may beentlfll done away with. i l r In thecase of ores in which the wine-t l? acid-soluble iron is small,theapplicalpllo of my mentioned discovery regarding l'he use of pressuremight result. in an uiidire progressive diminution in the total ironpresent, it having already been indicated that the presence of ferrousiron formed in means leach solutions is, in many cases, desirable byreason of its depolarizing action during subsequent electrolysis; but,when the presence of iron is not desired, my discovery regarding theeffects of pressure during heating may be utilized to free the solutiontherefrom as completely as may be desired. Any convenient means and anyconvenient time may be employed for the heating of the liquor; but Iprefer to apply pressure while t e liquors retain a degree of heat whichmay have been imparted to them to complete the leaching of the ore.

My second method of controlling excess of ferric iron, which I will nextdescribe, and which is especially suitable to cases in which the oredoes not carry considerable quantities of soluble iron, depends upon thefollowing facts. In electrolyzing by methods in which insoluble anodesof graphite are used in solutions carrying iron and cop per, the anodicefficiency of conversion of ferrous to ferric iron is at leastapproximately equal to the efficiency of copper deposition at thecathode. That is to say, two molecules of iron are oxidized orbroughtinto the ferric condition at the anode for each molecule of copperdeposited at the cathode. This may be accomplished by such precautionsas the employment of heat and circulatiom whereby the voltage is keptlow. Otherwise the anodic eiliciency may be lower, a high voltageresulting from ineflicient agitation, too high current density, or othercauses. When the anodic etliciency is thus lowered, there may he dangerof the disintegration of the graphite anode due to the free oxygenevolved.

With'lead anodes the anodic oxidation" ciliciency of ferrous to ferriciron is less than I when graphite is used, and the relative effi-Foregoing ciency at the anode as compared with thatat the cathode may bein the neighborhood of and anodic cliiciency with lead anodes may alsobe varied by changing the current density, the temperature, and the rateof circulation or agitation, or all of these 'fzictors. statements arealso true of i. solu-- ble anodes other than those mentioned, and,accordingly, whenever, in this description or in defining thisinvention, lead is specified as an anodic material, it is to beunderstood that other equivalent anodes maybe used, for example,compounds of iron and silicon.

Second method Making use of the above facts, I have discovered that, inthe electrolysis of copper solutions, the amount of ferric iron producedby regeneration from the ferrous form may often be satisfactorilycontrolled by merely varying the proportion of graphite to otherinsoluble anodic material employed in the electrolysis. That is to say,when the excess of ferrous iron accumulating in. successive cycles isnot too great, asma-y often be the case when mixed or sulfid oresare'trcated, a suitable proportioning of the comparatively eificientgraph ite anodes with anodes of less efficiency, such as lead anodes,can be relied uponto keep the netv ferric iron content constant for anynumber of leaching and electrolytic cycles, a gradually total ironcontent being meantime to accumulate as ferrous iron.

In practical operation, the approximate reducing power of an oredetermined, I prefer to provide, in any suit able electrolytic tankhouse, a predetermined suitable proportion of tanks or cells with leadanodes and tanks or cells with graphite anodes, it being advantageous toprovide an permitted increasing fraction of the,

body having been excess of, say lead anode tan s, of which a;

.grdater or variations in the ore may-require; and even when thequantities of iron content in the ore are such as toresult rapidincrease in the iron content of the leach liquors, so that the use of myfirst method is economically justified, I may sub sequently employ, asafurther refinement, my second above method for maintaining the desiredferric iron content of the regenerated leach liquor, the quantity ofcopperineantime recovered at the cathode with a given expenditure ofelectrical energy being practically unaffected by the character of theanode used.

The method of controlling ferric iron and its balance in successivecycles by varying the proportion of graphite and lead. anodes may bemore fully described. as follows.

in addition-thereto and v a lesser number may be used, as-

in a comparatively Graphite, as an anode, is very eiiicient,

lead anodes may be varied somewhat, but

usually about 60% eflicicn'cy may be had with lead anodes. That is to.say, of the oxygen set free at a leadanode 60% goes to oxidize ferrousiron in solution and the. re maining 40% is either freed as such or topcroxidize the lead. Now let us assume an ore that has such a proportionof oxide and sulphide copper that ferric iron equivalent to 80% duced bypassing the leaching solution through the ore. 'Obviously, in such acase if We use all leadanodes, We would have a constant deficiency offerric iron. in each cycle, and if on the other hand all graphite wasused with this particular ore, there would be a constant overproductionof fer but if a proportion of and half lead at 60% responding to the 80%reduced by the one of the copper deposited is reand the solutions wouldremain in balance with respect to the ferric iron. Other proportionsnuiy course be used as the character of the ores require, and in somecases either all lead or all graphite may be necessary.

In the preparation for the treatment of an ore by steps inrolviugg; mypresent invention I may treat a quantity of mixed ore, preferablydry-crushed to pass a quarterinch mesh, with a suitable leach iiquor;and this liquo may contain as much as 1% or more of l'erric iron in theform of ferric sulfate, about 2% iron as ferrous sulfate, free sulfuricacid up to about 5%, and increasing quantities of copper sulfate up toabout 4% of copper. I may bring the ore into contact with the successiveportions of leach liquor preferably applied on the countercurrentprinciple, and preferably employing only so much heat, during the latterportion of the period of extraction, as may be necessary to aneconomical recovery of values by the method which I have set forth andjustified in my copending application Ser, No. 639,969 filed May 18,1923 (Case B), the total quantity of leach liquor being prc erably keptapproximately constant.

sniping, then, that the iron content of the rich liquors obtained asabove is such as may result in subsequent inconvenience, and proceedingin accordance with the principles outiined, my present invention may beex amplified. by a subjecting oi' the rich liquors, by any convenientmeans, to additional heat to pressure sufiicient to effect, withoutneutralization, a satisfactory precipitation of iron componentstherefrom, the most favorable degree of heat and pressure for anyspecific ores hemp; best predetermined. by practical experience,

By suitable washing; of the precipitat cl i red above, may avoid any arm1 loss ot' copper therewith, all r is. water containing values beingpreferably combined with the richiiquors and subjected to electrolysisfor the deposition of copper l t regeneration oil a leach liquor.

ans

this the mentioned application of heat and pressure to effectprecipitation of iron may obviously be executed at any suitable theindicated cycle of operations, such precipitation shall im" step ofelectrolysis ion cl copper. thererred percentage of the rerrous oral orsubpls, if the oils con are .i e the necessity ol: *lstion dnriu thisapplication of sure, vcmploy the above" o! cd to brii r the liq-- ingrgraphite electrodes with, say, three cells containing lead electrodes,will result, upon an admixture of the residual liquor obtainedtherefrom, in a leach liquor ,con-

taining; the desired 131/ or more of ferric iron that may be regarded asfavorable to a complete extraction. of copper from certain mixed ores,it is obvious that the best ratio of graphite anode cells to lead anodecells may be regarded asdetermined by the experimental results abovesupposed for purposes of illustration.

It will, of course, be understood by those skilled in the art that bothof the described methods may be independently employed, and that variousmodifications may be made in either without departing from the spirit ofmy present invention as the same is indicated by the foregoingillustrative description and by the following claims.

What is claimed is:

1. In the recovery of copper from mixed copper ores containing iron, thestep which consists in applying heat and pressure to effect aprecipitation of iron from an acid solution.

2. In the recovery of copper from ores containing; also iron, the stepwhich consists in applying to a suitably warmed liquor suflicientpressure to precipitate an. iron compound therefrom.

In the recovery of copper from ores containing also iron,- the stepwhich consists in concurrently employing dissimilar anodes in suchproportion as to convert only a desired traction of the iron content ofa liquor undergoing electrolysis from a ferrous to a ferric formsuitable for use in a subsequent leaching operation.

4. In the recovery of copper from ores containing also iron, the stepwhich consists in applying to a suitably warmed liquor suflicientpressure to precipitate an iron com= pound. therefrom, and thenconcurrently employing dissimilar anodes in such pro portion. as toconvert a; desired fraction of the iron content of a liquor undergoingelectrolvsis into a ferric form. t in the recovery of copper from amixtil; containing iron by a cyclical process in which iron tends toaccumulate, the step wh consists in applying heat and pressure efficientto effect a desired precipitation of iron, said precipitate'heingwashable to avoid loss of values therewith.

'6. in the recovery of copper from a mixture containing iron by acyclical process 'in which iron tends to accumulate, the step whichconsists in applying heat and pres sure suihcient to eii'ect a desiredprecipita tionof iron, said precipitate being washable to avoi loss ofvalues therewith, and thereafter converting a desired proportion. ofiron from ferrous to a ferric condition while eiiecting anelectrodeposition oi copper.

7. To efieet without neutralization a pie cipitation of iron compoundsfrom acid solutions containing the same, the method which consists inapplying heat and pressure 5 simultaneously thereto. 4

y 8. To control'the extent of anodie oxidation effected during thecathodic electrodeposition of a metal, the method which consists inconcurrently employing dissimilar anodes in a predetermined ratio. 0

In testimony whereof I have signed my name to this specification.

GEORGE D. VAN ARSDALE.

